What I'm getting at is that single-user machines that host multiple VMs don't actually use much more CPU than they would if they ran what the VMs in aggregate a

What I'm getting at is that single-user machines that host multiple VMs don't actually use much more CPU than they would if they ran what the VMs in aggregate are running. The main difference, from a resource usage perspective, is that each VM needs RAM. I typically run at least two pfSense router VMs as VPN gateways. They use about 600MB each. And the Debian VM that I'm writing this in uses about 2.4GB. Most of that's used by the browser. But CPU usage is only about 10% of four 3GHz i5 cores. But if I stream some video, or download a torrent, all three VMs use more CPU. Altogether maybe 50%-60% CPU. That's because there are thee OpenVPN instances (one in the host, and one in each pfSense VM) encoding/decoding traffic. Even so, I doubt that it'd be all that different if there were no VMs, and the host was doing all that. In other words, I don't think that the VirtualBox overhead is all that high.